9 - reaction kinetics Flashcards
rate of reaction equation
change in conc/time for change to happen
vol of gas/time
gradient
y/x
where y is change is conc and x is change in time
collision theory
A + B –> C + D
in order for A to react with B they must collide and then they may react.
not all collisions will result in a reaction. there are two requirements:
- two molecules must react with sufficient energy (activation energy)
- must collide in the correct orientation
what is steric hindrance?
when the atoms in a molecule hinder the course of a reaction. if an atom or group of atoms is particularly large they can get in the way of n attacking species
what is the effect of concentration of a reaction?
for many reactions a higher conc means the frequency of collision between particles increases (bc they are closer together as there are more of them in a given vol of solution)
therefore more successful collisions
what is the effect of pressure on rate of reaction?
in the gas phase, increase in pressure will increase the rate of reaction
more reactant molecules in a given volume of mixture - frequency of collisions increases
changing pressure has virtually no effect for solids and liquids
what is the effect of surface area on rate of reaction?
for heterogeneous reactions involving a solid, large sa will increase rate of reaction
effectiveness of solid catalysts is also improved when they are finely divided
how does temperature change affect on rate of reaction?
increase increases the fraction of molecules that possess the required Ea. rate of reaction increases.
on MB curve higher temp is lower and further right
what are collisions in solution like?
in gas phase, molecules move at high speeds and frequently collide
in solution, molecules are closely packed together, in low-medium concs, most of the solution is solute
there are two stages to a reaction in solution
- all molecules have to come together, by a process of diffusion, into the same solvent cage
- they react
effect of a catalyst on a reaction
works by providing an alternative route for the reaction - has a lower Ea than the original route
on MB curve shown as a line to the left of the Ea line
reaction profile diagram with a cataylst features a lower catalyst curve
what are two economic advantages of catalysts in industry?
- increase rate f chemical reaction meaning more of the desired product is made in a given time
- reactions can take place at lower temps resulting in a decrease in the energy costs to the manufacturer
catalysts in industry info
most are heterogenous (in a diff phase to that of the reactant) - solids are commonly used
